Comparison of salt tolerance between sugar beet M14 and Beta vulgaris L.

Objectives Sugar beet is tolerant to salt and alkali. We compared the salt tolerance of two high quality materials so as to provide reference for its breeding.

Methods A hydroponic culture experiment was conducted under normal and 200 mmol/L NaCl stress condition, the tested two sugar beet materials were M14 strain (18+1 chromosomes) and the diploid (18 chromosomes) from the same parent. At 0, 1, 3, 5 and 7 days after treatment, plant samples were collected, the plant height and root length were measured, the contents of K⁺, Na⁺, MDA and betaine in the roots were determined, the transcription levels of main antioxidant enzyme genes (SOD, CAT, APX, GR) and betaine synthesis genes (CMO, BADH) and their genes encoding enzyme activities were measured.

Results 1) Under normal condition, there was no significant difference in plant height and root length between the two beet materials; under 200 mmol/L NaCl stress, the plant height and root length of the M14 were higher than those of diploid. 2)Under normal condition, the M14 and diploid had similar K⁺ and Na⁺ absorption capacity, and produced equivalent amount of betaine during metabolism; under 200 mmol/L NaCl stress, the two materials absorbed similar amount of K⁺ and Na⁺ in roots, but M14 synthesized higher betaine content in roots than diploid did. 3) Under normal condition, the transcription level of SOD, CAT, APX, GR, CMO and BADH in the roots of two beet materials were not significantly different; under 200 mmol/L NaCl stress, the transcription levels of SOD and GR genes in the roots of M14 were higher than those of diploid at the first day of treatment, and the transcriptional levels of CAT, APX, CMO and BADH genes were significantly higher than those of diploid from 3 to 5 days of treatment. 4) Under normal condition, the differences in activities of SOD, CAT, APX, GR, CMO and BADH between M14 and diploid roots were not significant; under 200 mmol/L NaCl stress, the activities of all tested enzymes in the roots of M14 were significantly higher than those of diploid.

Conclusions Under 200 mmol/L NaCl stress, the roots of M14 have higher betaine content, transcription levels of antioxidant and betaine synthesis genes, and higher activities of these encoding enzymes, so M14 is more tolerant to salt stress than the diploid .